In recent years, demands for transportation fuels, especially gasoline goods, have continuously increased, but demands for heavy oil goods such as bunker oil have decreased. However, the lack of high-quality crude oil results in an increase in percentage of high-sulfur and heavy crude oil in the crude oil currently being produced. In addition, with concerns about the dearth of petroleum resources, the need to develop technology for preparing light petroleum goods and distillates of petrochemical raw materials having a higher added value by upgrading inexpensive heavy hydrocarbon distillate such as bitumen that is a substitute for crude oil, and heavy fraction, which are produced during refinement of crude oil, is continuously being proposed.
Representative examples of such low-grade heavy distillate (heavy hydrocarbon distillate) includes vacuum residues which are bottom distillates in a vacuum distillation column (for example, those which are obtained at a pressure of approximately 25 to 100 mmHg and have an atmospheric equivalent boiling point of approximately 813.15 K or higher) during a process of refining crude oil. Since such low-grade heavy distillates have a low H/C ratio and a high viscosity property, they may not be upgraded easily. Also, the heavy hydrocarbon distillate, especially vacuum residues, typically have high contents of sulfur compounds, nitrogen compounds, oxygen compounds and heavy metals (vanadium, nickel, iron, and the like), as well as components having condensed polyaromatic rings such as asphaltene.
In this regard, various methods of upgrading the heavy hydrocarbon distillate have been proposed. By way of example, a process of converting a low-grade heavy hydrocarbon distillate or a high boiling point distillate into a higher value-added distillate having a lower boiling point has been proposed. Examples of the above-described conversion process include a cracking process, a hydrocracking process, a catalytic cracking process, and a steam cracking process. However, the above-described conversion process involves severe operating conditions such as high-temperature and high-hydrogen pressure conditions, and a hydration catalyst using a weakly acidic support is used to inhibit formation of cokes.
Meanwhile, a method of treating and upgrading crude oil or heavy hydrocarbon distillate in a supercritical medium or solvent is currently being developed. For example, a method of recovering distillate having a reduced content of asphaltene, sulfur compounds, nitrogen compounds or metals as well as of a reduced content of heavy components by bringing a stream of heavy hydrocarbon distillate into contact with water in a supercritical state to convert the stream of heavy hydrocarbon distillate into a reformed heavy fraction (Korean Unexamined Patent Application Publication No. 2010-0107459, etc.), a method of decomposing a heavy hydrocarbon distillate under supercritical conditions of a solvent such as an aliphatic hydrocarbon (dodecane, normal hexane, cyclohexane, etc.) (Japanese Unexamined Patent Application Publication No. 2008-297468, etc.), and a method of converting high boiling point hydrocarbon distillate such as residues into low boiling point hydrocarbon distillate under supercritical conditions of an acid solution using a halogen or hydrogen halide as a catalyst (U.S. Pat. No. 4,559,127, etc.) are known in the related art.
Most of the methods known in the prior art are methods of converting heavy hydrocarbon distillate into low boiling point hydrocarbon distillate in the presence of a catalyst using water or an aliphatic hydrocarbon solvent as a supercritical medium. In this case, representative higher added value hydrocarbon distillate which can be obtained from the upgrading process include naphtha (boiling point: IBP to 177° C.), and middle distillates (boiling point: 177 to 343° C.). However, when a solvent for supercritical media according to the prior art is used, the heavy hydrocarbon distillate may be converted into naphtha and middle distillates, but a large amount of gas oil, residues etc are obtained. Therefore, this process has limits in enhancing a rate of conversion into a low boiling point distillates (i.e., a light fraction) such as naphtha and middle distillates. Also, since there is a high change in compositions of the hydrocarbon distillates converted at a hydrogen pressure, this conversion process has a problem in that it should be performed at a relatively high hydrogen partial pressure to convert the heavy hydrocarbon distillate into the higher added value distillates such as low boiling point distillates (for example, naphtha and middle distillates).
Therefore, an operating procedure may be performed under a lower hydrogen pressure condition than in the prior art, and there is a need for a pretreatment process capable of maximizing recovery of the low boiling point distillates such as naphtha or middle distillates.
Also, the need for alternative energy has been increasingly required with exhaustion of fossil fuels. Therefore, lignocellulosic biomasses which can be converted into energy have been issued as important resources. Lignocellulosic biomasses accounting for a majority of biomasses present on the Earth have attracted attention as useful resources, which are produced at an amount of 107 ton every year all over the world. The lignocellulosic biomasses are expected to replace petroleum since it can be subjected to glycosylation and fermentation to produce useful materials such as fuels (for example, bioethanol, etc.) and chemical derivatives while carbon dioxide is emitted at the same time. According to the “Global Biofuels Outlook 2007,” the biofuel promoting policies were adopted by 40 of 50 countries surveyed, and an act of introduction of biofuels was legislated in 27 countries.
Among the lignocellulosic biomasses, lignocellulose is known as a composite consisted of cellulose (40 to 50%), hemicellulose (25 to 35%) and lignin (15 to 20%). In glycosylation of lignocellulosic biomasses, it is very difficult but important to decompose non-degradable cellulose so as to produce glucose with high efficiency. This is because glucose becomes a main fermentation source to produce biofuels, various compounds and biomaterials. However, an enzyme for glycosylation of cellulose (i.e., a cellulase) does not easily gain access to the lignocellulosic biomasses since cellulose is firmly surrounded by lignin and hemicellulose and has a crystal structure. Therefore, the lignocellulosic biomasses show a glycosylation rate of less than 20% of the theoretical yield when they do not undergo a pretreatment process for removing lignin and hemicellulose and collapsing the crystal structure of cellulose.
Dilute acid pretreatment used for pretreatment of lignocellulose, ammonia fiber expansion (AFEX) and hot water pretreatment have problems in that reactions at a high temperature, the use of toxic materials and solvents, and generation of by-products result in hindrance to a subsequent biological conversion process. Hence, a separate neutralization process should be performed after pretreatment, which results in an increase in additional costs.
Therefore, there is a demand to develop technology for removing/decomposing lignin and destructuring cellulose as basic technology through analysis and identification of the molecular structure of lignocellulose.